The present invention relates to a method of controlling a numerically controlled machine tool such as a milling machine, machining center or electric discharge machine having a plurality of feed shafts of three orthogonal axes of X, Y and Z or having a plurality of feed shafts of at least one of the rotary shafts of axes of A, B and C in addition to the three orthogonal axes of X, Y and Z. Further, the present invention relates to a 15 numerically controlled machine tool. In other words, the present invention relates to a new technique of a numerically controlled machine tool by which a workpiece can be machined with high accuracy even at a high feed speed.
Concerning a numerically controlled machine tool, it is required that a workpiece is accurately machined in a short period, that is, it is required that a workpiece is highly efficiently and accurately machined. In general, it is known that machining accuracy is deteriorated when the feed speed of a machine tool is raised. This deterioration in machining accuracy is caused by a lost motion of the feed shaft and a delay of servo-control of the numerically controlled machine tool. Therefore, in the case of a numerically controlled machine tool, in order to conduct machining with high accuracy even when the feed speed is raised to a high value, backlash of the feed shaft is corrected and further friction of the feed shaft is corrected, and furthermore speed adjusting control of the feed shaft is conducted according to the weight of a workpiece and the temperature of the feed shaft motor. For example, the following prior arts are provided.
The first prior art is disclosed in Japanese Patent Publication No. 2606773, which discloses an acceleration control method and device in a servo system. According to this prior art, lost motions of the feed shaft caused by backlash, elastic deformation and static friction in the case of inversion in the direction of movement of the feed shaft are corrected by conducting the most appropriate acceleration control corresponding to the respective characteristics so as to reduce the deterioration of machining accuracy. To accomplish the above object, the first, second and third acceleration for compensating the lost motions caused by backlash, elastic deformation and static friction in the feed system are added to the speed commands of the servo control unit, so that the delay caused by the lost motions can be immediately made up.
The second prior art is a servo motor control method disclosed in Japanese Patent Publication No. 2709969.
According to this method, for the object of conducting the most appropriate backlash correction even when the cutting condition fluctuates, the target value is set at a value, the sign of which is reverse to that, of the integrator of the speed control unit before the direction of movement is inverted, and a value obtained when the value of the integrator of the speed control unit is subtracted from the target value is multiplied by a constant, and the thus obtained value is made to be a value of backlash acceleration in the speed control unit, for example, a value obtained when a value proportional to the square root of a positional deviation at the moment when the direction of movement is inverted is multiplied, and the thus obtained value is made to be a value of backlash acceleration in the speed control unit.
The third prior art is a method and device of controlling acceleration and deceleration of a machine tool disclosed in Japanese Unexamined Patent Publication No. 11-90769. According to this prior art, for the object of ensuring high machining accuracy and shortening the machining time when the weights of moving things such as a tool and a workpiece are changed in the case of replacing them, the drive system is controlled by an acceleration corresponding to the rigidity of the machine tool, machining accuracy (allowable error) and weight of the workpiece. That is, there is disclosed a technique in which the acceleration is changed corresponding to the load inertia which has been previously set.
The fourth prior art is a speed control unit of a servo motor disclosed in Japanese Unexamined Patent Publication No. 6-274763. This patent publication describes a torque observer by which the load torque is estimated from the output torque of the feed shaft motor and the acceleration of an object to be driven.
According to this technique, a change in the estimated value of the load torque is detected, and the load inertia is estimated, and then the load inertia which has been set in the torque observer is renewed.
The fifth prior art is a method and device of controlling a numerically controlled device disclosed in Japanese Patent Publication No. 2853023. According to this technique, for the object of preventing the feed shaft motor from overheating even when the motor is continuously operated being frequently accelerated and decelerated because the feed shaft is quickly rotated, the temperature of the feed shaft motor is measured, and the thus measured temperature is compared with the predetermined temperature data allowed to the feed shaft motor. According to the result of comparison, the acceleration and the deceleration curve of the feed shaft are controlled being changed.
According to the first prior art, the acceleration is found, and the thus found acceleration is added to a speed command value of the servo control unit. In a numerically controlled machine tool, which is actually used, it is finally required that how high torque command value or how high electric current command value is outputted to the feed shaft motor drive means. Therefore, when the speed command value in the middle of servo control is changed like the first prior art, a delay is caused when the command value is converted into a torque command value or an electric current command value and arrives at the feed shaft motor drive means.
According to the second prior art, the backlash acceleration calculated according to the positional deviation is made to be a backlash acceleration in the speed control unit. Therefore, a delay still exists in the servo system composed of a positional feedback control means and speed feedback control means.
According to the third prior art, the load inertia is previously set at a predetermined value. Therefore, the acceleration is changed according to the weight of a workpiece. That is, when the weight of a workpiece is heavy, the acceleration is raised to an allowable limit, and when the weight of a workpiece is light, the acceleration is lowered. When the acceleration is lowered, the machining efficiency is deteriorated.
The fourth prior art relates to a torque observer for estimating the load torque of a common servo motor. The load torque is estimated according to the speed command value, and the load inertia is estimated according to the estimated load torque. Then, the estimated load inertia is sent to the transfer function of the mechanical system so as to conduct feed control. According to the aforementioned technique, since the load inertia is an estimated value, a delay is caused in the feed shaft of the device, and the machining accuracy is affected by the delay.
According to the fifth prior art, the time constant of acceleration and deceleration is controlled in accordance with the temperature of the feed shaft motor, so that the feed shaft motor is prevented from overheating without changing the command feed speed. When this technique is adopted, it is possible to prevent the feed shaft motor from overheating, however, the time constant of acceleration and deceleration is increased, and the machining accuracy is deteriorated.
Other than the above prior arts, there are provided conventional methods in which correction of backlash or correction of friction is conducted. However, according to these conventional methods, the same correction value is used without giving consideration to the speed and acceleration of a moving object. In the case of an actual machining operation, when an object of the same profile is machined at a different feed speed, the dimension of machining changes when the conventional correction is conducted. When a curved face, the radius of curvature of which is different, is machined over a plurality of quadrants, the feed speed of at least one feed shaft once becomes zero in the case of changing over the quadrant. After that, the direction of the feed speed is inverted. Therefore, an acceleration is generated. In this case, the acceleration is changed by the radius of curvature. When the conventional correcting method is applied to the aforementioned case, the machining size is changed. That is, in the case of inverting a direction of movement and also in the case of starting a movement after a temporary stoppage, it is necessary to conduct correction of friction according to the speed and acceleration of a moving object.
Concerning the value of load inertia of the conventional numerically controlled device, for example, the value of load inertia in the case of loading a workpiece, the weight of which is half of the weight of a maximum workpiece to be loaded, is adopted as a constant value. A value found when this constant value is multiplied by the acceleration at each time is outputted to the feed motor drive means as a torque command. Under the above controlling condition, even if the load inertia is increased when a heavy work is loaded, it is impossible to generate a necessary torque command. Therefore, the actual movement of the feed shaft is delayed with respect to the movement command. Even if the load inertia is decreased when a light workpiece is loaded, a torque command, which is unnecessarily high, is generated, so that the moving body is given a shock. As a result, the feed speed fluctuates, and machining can not be performed with accuracy and the thus obtained profile is deteriorated. Further, although the weight of a workpiece changes every second, that is, although the load inertia changes, the torque command is kept constant. In other words, servo control can not follow the load condition which changes every second. As a result, the machining accuracy is changed.
The present invention has been accomplished to solve the above problems of the prior art. It is an object of the present invention to provide a method of controlling a numerically controlled machine tool. Also, it is an object of the present invention to provide a numerically controlled machine tool capable of conducting machining with high accuracy even if a moving object of the machine is moved at high speed.
It is another object of the present invention to enhance the machining accuracy in the case of machining a profile or a curved face by moving a plurality of feed shafts simultaneously.
It is still another object of the present invention to conduct machining with high accuracy by giving consideration to a change in the dynamic frictional force and also a change in the static frictional force in the case of inverting a direction of movement of the feed shaft and also in the case of starting a movement from a stoppage.
It is still another object of the present invention to conduct machining with high accuracy by giving consideration to a change in the weight when a workpiece loaded on the moving body of the feed shaft or an attachment is replaced or when a workpiece is machined so that the weight of the workpiece is reduced with time.
It is still another object of the present invention to conduct machining highly efficiently with high accuracy without the occurrence of overheat of the feed shaft motor even if the feed shaft motor is continuously operated while it is frequently accelerated and decelerated.
In order to accomplish the above objects, the present invention is composed as follows. By using the execution result of the numerically controlled program data obtained from the servo control unit of the numerically controlled device, a desired torque command or an electric current command, which corresponds to a change in the frictional force of the feed mechanism of the feed shaft or corresponds to a change in a workpiece, is estimated by calculation, and the thus obtained estimation value is outputted to the feed motor drive means.
According to the present invention, there is provided a method of controlling a numerically controlled machine tool having a plurality of feed shafts of three orthogonal X-Y-, and Z-axes or at least one of rotary shafts of A-, B- and C-axes in addition to a plurality of feed shafts of three orthogonal X-, Y-, and Z-axes of X, characterized in that the method comprises the steps of:
taking numerical controlling program data from a reading and interpreting unit provided in a numerically controlling device to execute the program data in a movement command distribution controlling unit and a servo control unit;
estimating an appropriate torque or electric current command corresponding to the changes in frictional force in the feed mechanisms of the respective feed shafts or in the weight of a workpiece based on the results of execution of the numerically controlling program data outputted from the servo control unit;
outputting the estimated appropriate torque or electric current command to motor drive means of the feed shafts; and
driving feed motors by the appropriate torque or electric current command corresponding to the changes in frictional force in the feed mechanisms of the respective feed shafts or in the weight of a workpiece.
According to the present invention, there is provided a method of controlling a numerically controlled machine tool including the steps of taking numerical controlling program data from a reading and interpreting unit provided in a numerically controlling device to execute the program data in a movement command distribution controlling unit and a servo control unit; and outputting the execution to motor drive means of the feed shafts through feed shaft motor driving means to move a moving body by a feed mechanism, characterized in that the method comprises the steps of:
calculating a torque or electric current command, based on a moving command value outputted from the movement command distribution controlling unit, in the servo control unit to output to the feed motor driving means to drive the feed motor;
taking the torque or electric current command outputted from the servo motor control unit to the feed shaft motor driving means;
estimating a desired torque or electric current command corresponding to the changes in frictional force in the feed mechanisms of the respective feed shafts or in the weight of a workpiece based on the results of execution of the numerically controlling program data outputted from the servo control unit;
outputting the estimated desired torque or electric current command to motor drive means of the feed shafts; and
Estimation of the desired torque or electric current command corresponding to the changes in frictional force in the feed mechanisms or in the weight of a workpiece is an estimation of a torque or electric current command corresponding to the changes in frictional force in the feed mechanisms or in the weight of a workpiece based on the torque or electric current command and the acceleration of the feed shaft, which have been taken.
Further, according to the present invention, there is provided a method of controlling a numerically controlled machine tool including the steps of taking numerical controlling program data from a reading and interpreting unit provided in a numerically controlling device to execute the program data in a movement command distribution controlling unit and a servo control unit; and outputting the execution to motor drive means of the feed shafts through feed shaft motor driving means to move a moving body by a feed mechanism, characterized in that the method comprises the steps of:
calculating a torque or electric current command, based on a moving command value outputted from the movement command distribution controlling unit, in the servo control unit to output to the feed motor driving means to drive the feed motor;
detecting an inversion of the direction of movement of the feed shaft;
calculating the acceleration of the feed shaft at the time when he inversion of the direction of movement of the feed shaft is detected;
calculating the load torque based on the torque electric current command outputted from the servo control unit at the time when the inversion of the direction of movement of the feed shaft is detected to set it as the load torque before the inversion of the direction of movement of the feed shaft;
inverting the sign of value of the load torque and multiplying the load torque before the inversion of the direction of movement of the feed shaft by a predetermined constant to set the product as a target value for the load torque for the operation after the inversion of the direction of movement of the feed shaft;
calculating a load torque for the operation after the direction of movement of the feed shaft is inverted, between the time of the detection of the inversion of the direction of movement of the feed shaft and the time when the load torque reaches the target value, by using a time constant expressed as a function of acceleration at the time of the inversion of the direction of the feed shaft;
calculating a desired torque or electric current command based on the load torque after the direction of movement of the feed shaft is inverted;
outputting the desired torque or electric current command to motor drive means of the feed shafts; and
moving the moving body by the feed shaft motor and the feed mechanism.
The load torque after the inversion of the direction of movement of the feed shaft may be calculated by using a time constant which is in inverse proportion to square root of the acceleration at the time when the inversion of the direction of movement of the feed shaft is detected.
The calculation of the load torque after the inversion of the direction of movement of the feed shaft can be terminated by a ratio until the set point of load torque reaches or by a distance from the feed shaft when an inversion of the direction of movement of the feed shaft is detected.
Further, according to the present invention, there is provided a method of controlling a numerically controlled machine tool including the steps of taking numerical controlling program data from a reading and interpreting unit provided in a numerically controlling device to execute the program data in a movement command distribution controlling unit and a servo control unit; and outputting the execution to motor drive means of the feed shafts through feed shaft motor driving means to move a moving body by a feed mechanism, characterized in that the method comprises the steps of:
setting previously a desired torque command and a speed command or a desired electric current command and a speed command, depending on the static frictional force in the feed mechanism;
calculating a torque or electric current command, based on a moving command value outputted from the movement command distribution controlling unit, in the servo control unit to output to the feed motor driving means to drive the feed motor;
detecting an inversion of the direction of movement of the feed shaft or an initiation of movement of the stationary feed shaft;
outputting, when the inversion of the direction of movement of the feed shaft or the initiation of movement of the stationary feed shaft is detected, the desired torque command and the speed command or the desired electric current command and the speed command, which are previously set, to the feed shaft motor driving means and servo control means; and
moving the moving body by the feed shaft motor and feed mechanism.
Further, according to the present invention, there is provided a method of controlling a numerically controlled machine tool including the steps of taking numerical controlling program data from a reading and interpreting unit provided in a numerically controlling device to execute the program data in a movement command distribution controlling unit and a servo control unit; and outputting the execution to motor drive means of the feed shafts through feed shaft motor driving means to move a moving body by a feed mechanism, characterized in that the method comprises the steps of:
setting previously a desired torque command and a speed command or a desired electric current command and a speed command, depending on the static frictional force in the feed mechanism;
calculating a torque or electric current command, based on a moving command value outputted from the movement command distribution controlling unit, in the servo control unit to output to the feed motor driving means to drive the feed motor;
detecting an inversion of the direction of movement of the feed shaft or an initiation of movement of the stationary feed shaft;
calculating the acceleration of the feed shaft at the time when the inversion of the direction of movement of the feed shaft is detected;
calculating the load torque based on the torque electric current command outputted from the servo control unit at the time when the inversion of the direction of movement of the feed shaft is detected to set it as the load torque before the inversion of the direction of movement of the feed shaft;
inverting the sign of value of the toad torque and multiplying the load torque before the inversion of the direction of movement of the feed shaft by a predetermined constant to set the product as a target value for the load torque for the operation after the inversion of the direction of movement of the feed shaft;
calculating a load torque for the operation after the direction of movement of the feed shaft is inverted, between the time of the detection of the inversion of the direction of movement of the feed shaft and the time when the load torque reaches the target value, by using a time constant expressed as a function of acceleration at the time of the inversion of the direction of the feed shaft;
calculating a desired torque or electric current command based on the load torque after the direction of movement of the feed shaft is inverted;
outputting the desired torque or electric current command to motor drive means;
outputting, when the inversion of the direction of movement of the feed shaft or the initiation of movement of the stationary feed shaft is detected, the desired torque command and the speed command or the desired electric current command and the speed command, which are previously set, to the feed shaft motor driving means and servo control means; and
moving the moving body by the feed shaft motor and feed mechanism.
Further, according to the present invention, there is provided a method of controlling a numerically controlled machine tool including the steps of taking numerical controlling program data from a reading and interpreting unit provided in a numerically controlling device to execute the program data in a movement command distribution controlling unit and a servo control unit; and outputting the execution to motor drive means of the feed shafts through feed shaft motor driving means to move a moving body by a feed mechanism, characterized in that the method comprises the steps of:
calculating a torque or electric current command, based on a moving command value outputted from the movement command distribution controlling unit, in the servo control unit to output to the feed motor driving means to drive the feed motor;
taking the torque or electric current command outputted to the feed shaft motor drive means through the servo control unit as a torque or electric current command for the moving feed shaft;
calculating a load inertia based on the torque or electric current command for the moving feed shaft and the acceleration in the feed shaft;
calculating a desired torque or electric current command corresponding to the calculated load inertia;
outputting the desired torque or electric current command to the feed motor shaft motor drive means; and
moving the moving body by the feed shaft motor and the feed mechanism.
Further, according to the present invention, there is provided a method of controlling a numerically controlled machine tool including the steps of taking numerical controlling program data from a reading and interpreting unit provided in a numerically controlling device to execute the program data in a movement command distribution controlling unit and a servo control unit; and outputting the execution to motor drive means of the feed shafts through feed shaft motor driving means to move a moving body by a feed mechanism, characterized in that the method comprises the steps of:
calculating a torque or electric current command, based on a moving command value outputted from the movement command distribution controlling unit, in the servo control unit to output to the feed motor driving means to drive the feed motor;
detecting the weight of a workpiece or a moving body to which the workpiece is mounted;
calculating a load inertia based on the detected weight;
calculating a desired torque or electric current command based on the calculated load inertia;
outputting the desired torque or electric current command to the speed shaft motor drive means; and
moving the moving body by the feed shaft motor and the feed mechanism.
Further, according to the present invention, there is provided a method of controlling a numerically controlled machine tool including the steps of taking numerical controlling program data from a reading and interpreting unit provided in a numerically controlling device to execute the program data in a movement command distribution controlling unit and a servo control unit; and outputting the execution to motor drive means of the feed shafts through feed shaft motor driving means to move a moving body by a feed mechanism, characterized in that the method comprises the steps of:
calculating a torque or electric current command, based on a moving command value outputted from the movement command distribution controlling unit, in the servo control unit to output to the feed motor driving means to drive the feed motor;
setting and storing a time constant of acceleration and deceleration of the feed shaft and allowable temperature data for feed shaft motor;
taking the torque or electric current command outputted from the servo control unit to the feed motor driving means;
estimating the temperature of the feed shaft motor based on the taken torque or electric current command;
comparing the previously stored allowable temperature data and the estimated temperature of the feed shaft motor;
calculating an acceleration or deceleration time constant based on the comparison results;
estimating a desired torque command or an electric current command corresponding to a change in the frictional force of the feed mechanism or the weight of a workpiece obtained based on the torque command or the electric current command and the acceleration of the feed shaft outputted from the servo control unit to the feed shaft motor drive means;
outputting the estimated desired torque or electric current command to the feed motor drive means; and
moving the moving body by the feed shaft motor and the feed mechanism.
Further, according to the present invention, there is provided a numerically controlled machine tool having a plurality of feed shafts of three orthogonal X-, Y-, and Z-axes or at least one of rotary shafts of A-, B- and C-axes in addition to a plurality of feed shafts of three orthogonal X-, Y-, and Z-axes, characterized in that the numerically controlled machine tool comprises:
a feed mechanism for moving a moving body of each feed shaft;
a feed shaft motor for driving the feed mechanism;
a feed shaft motor drive means for driving the feed shaft motor;
a numerically controlling means for executing the numerically controlled program data to drive the feed shaft motor by a moving command distribution controlling unit and a servo control unit and for outputting the result of execution to the feed shaft motor through the feed shaft motor drive means;
a calculation controlling means for estimating a desired torque command or an electric current command corresponding to a change in the frictional force of the feed mechanism or the weight of a workpiece obtained based on the torque command or the electric current command and the acceleration of the feed shaft outputted from the servo control unit to the feed shaft motor drive means when the feed shaft motor is driven to output the estimated desired torque or electric current command to the feed motor drive means.
Further, according to the present invention, there is provided a numerically controlled machine tool including a numerically controlling device which has a reading and interpreting unit, a movement command distribution controlling unit for executing a numerical control program data, which has been drawn from the reading and interpreting unit, the result of execution being outputted to a feed shaft motor of a feed shaft through a feed shaft motor drive means to move a moving body by a feed mechanism, characterized in that the numerically controlled machine tool comprises:
a feed mechanism for moving a moving body of each feed shaft;
a feed shaft motor for driving the feed mechanism;
a feed shaft motor drive means for driving the feed shaft motor;
a numerically controlling means for executing the numerically controlled program data to drive the feed shaft motor by a moving command distribution controlling unit and a servo control unit and for outputting the result of execution to the feed shaft motor through the feed shaft motor drive means;
a calculation controlling means for estimating a desired torque command or an electric current command corresponding to a change in the frictional force of the feed mechanism or the weight of a workpiece obtained based on the torque command or the electric current command and the acceleration of the feed shaft outputted from the servo control unit to the feed shaft motor drive means when the feed shaft motor is driven to output the estimated desired torque or electric current command to the feed motor drive means.
Further, according to the present invention, there is provided a numerically controlled machine tool including a numerically controlling device which has a reading and interpreting unit, a movement command distribution controlling unit for executing a numerical control program data, which has been drawn from the reading and interpreting unit, the result of execution being outputted to a feed shaft motor of a feed shaft through a feed shaft motor drive means to move a moving body by a feed mechanism, characterized in that the numerically controlled machine tool comprises:
a position control means for calculating a speed command based on a movement command of the feed shaft outputted from the movement command distribution controlling means;
a speed control means for calculating a torque command or an electric current command based on the speed command of the feed shaft outputted from the position control means;
a feed shaft motor drive means for outputting an electric current to drive the feed shaft motor according to the torque command of the feed shaft or the electric current command outputted from the speed control means;
a detecting means for detecting an inversion of the direction of movement of the feed shaft;
an acceleration calculating means for calculating an acceleration when an inversion of the direction of movement of feed shaft by the detecting means; and
a load torque calculating means for calculating a load torque after the inversion of the direction of movement of the feed shaft by using a time constant expressed by a function of the torque command or the electric current command outputted from the speed control means at the time when the inversion of the direction of movement of the feed shaft is detected by the detecting means and the acceleration, calculated by the acceleration calculating means, when the inversion of the direction of movement of the feed shaft is detected to output the calculated desired torque or electric current command corresponding to the load torque to the speed control means.
Further, according to the present invention, there is provided a numerically controlled machine tool including a numerically controlling device which has a reading an interpreting unit, a movement command distribution controlling unit for executing a numerical control program data, which has been drawn from the reading an interpreting unit, the result of execution being outputted to a feed shaft motor of a feed shaft through a feed shaft motor drive means to move a moving body by a feed mechanism, characterized in that the numerically controlled machine tool comprises:
a position control means for calculating a speed command based on a movement command of the feed shaft outputted from the movement command distribution controlling means;
a speed control means for calculating a torque command or an electric current command based on the speed command of the feed shaft outputted from the position control means;
a feed shaft motor drive means for outputting an electric current to drive the feed shaft motor according to the torque command of the feed shaft or the electric current command outputted from the speed control means;
a detecting means for detecting an inversion of the direction of movement of the feed shaft or the initiation of movement of the stationary feed shaft; and
a static friction correcting means for outputting predetermined desired torque command and speed command or electric current command and speed command, to the feed shaft motor drive means and the speed control means, corresponding to the static frictional force of the feed mechanism when the inversion of the direction of movement of the feed shaft or the initiation of the movement of the feed shaft is detected by the detecting means.
Further, according to the present invention, there is provided a numerically controlled machine tool including a numerically controlling device which has a reading and interpreting unit, a movement command distribution controlling unit for executing a numerical control program data, which has been drawn from the reading and interpreting unit, the result of execution being outputted to a feed shaft motor of a feed shaft through a feed shaft motor drive means to move a moving body by a feed mechanism, characterized in that the numerically controlled machine tool comprises:
a position control means for calculating a speed command based on a movement command of the feed shaft outputted from the movement command distribution controlling means;
a speed control means for calculating a torque command or an electric current command based on the speed command of the feed shaft outputted from the position control means;
a feed shaft motor drive means for outputting an electric current to drive the feed shaft motor according to the torque command of the feed shaft or the electric current command outputted from the speed control means;
a detecting means for detecting an inversion of the direction of movement of the feed shaft or the initiation of movement of the stationary feed shaft; and
an acceleration calculating means for calculating the acceleration when the detecting means detects the inversion of the direction of movement of the feed shaft;
a load torque calculating means for calculating a load torque after the inversion of the direction of movement of the feed shaft by using a time constant expressed by a function of the torque command or the electric current command outputted from the speed control means at the time when the inversion of the direction of movement of the feed shaft is detected by the detecting means and the acceleration, calculated by the acceleration calculating means, when the inversion of the direction of movement of the feed shaft is detected to output the calculated desired torque or electric current command corresponding to the load torque to the speed control means;
a static friction correcting means for outputting predetermined desired torque command and speed command or electric current command and speed command, to the feed shaft motor drive means and the speed control means, corresponding to the static frictional force of the feed mechanism when the inversion of the direction of movement of the feed shaft or the initiation of the movement of the feed shaft is detected by the detecting means.
Further, according to the present invention, there is provided a numerically controlled machine tool including a numerically controlling device which has a reading an interpreting unit, a movement command distribution controlling unit for executing a numerical control program data, which has been drawn from the reading an interpreting unit, the result of execution being outputted to a feed shaft motor of a feed shaft through a feed shaft motor drive means to move a moving body by a feed mechanism, characterized in that the numerically controlled machine tool comprises:
a position control means for calculating a speed command based on a movement command of the feed shaft outputted from the movement command distribution controlling means;
a speed control means for calculating a torque command or an electric current command based on the speed command of the feed shaft outputted from the position control means;
a feed shaft motor drive means for outputting an electric current to drive the feed shaft motor according to the torque command of the feed shaft or the electric current command outputted from the speed control means;
a speed feedforward control means for estimating a speed command based on the movement command of the feed shaft outputted from the movement command distribution controlling unit by calculation to output the speed command to the speed control means;
an acceleration feedforward control means for estimating an acceleration or torque command of the feed shaft outputted from the movement command distribution controlling unit by calculation to output the acceleration or torque command to the feed shaft motor drive means; and
an inertia calculating means for calculating a load inertia based on the torque or electric current command, outputted to the feed shaft motor drive means from the speed control means, and the acceleration of the feed shaft to output the load inertia to the speed control means and the acceleration feed forward control means, the speed control means outputs a desired torque or electric current command based on the load inertia, calculated by the inertia calculating means, to the feed shaft motor drive means.
Further, according to the present invention, there is provided a numerically controlled machine tool including a numerically controlling device which has a reading and interpreting unit, a movement command distribution controlling unit for executing a numerical control program data, which has been drawn from the reading and interpreting unit, the result of execution being outputted to a feed shaft motor of a feed shaft through a feed shaft motor drive means to move a moving body by a feed mechanism, characterized in that the numerically controlled machine tool comprises:
a position control means for calculating a speed command based on a movement command of the feed shaft outputted from the movement command distribution controlling means;
a speed control means for calculating a torque command or an electric current command based on the speed command of the feed shaft outputted from the position control means;
a feed shaft motor drive means for outputting an electric current to drive the feed shaft motor according to the torque command of the feed shaft or the electric current command outputted from the speed control means;
a speed feedforward control means for estimating a speed command based on the movement command of the feed shaft outputted from the movement command distribution controlling unit by calculation to output the speed command to the speed control means;
an acceleration feedforward control means for estimating an acceleration or torque command of the feed shaft outputted from the movement command distribution controlling unit by calculation to output the acceleration or torque command to the feed shaft motor drive means;
a weight detecting means for detecting the weight of a workpiece or a moving body to which the workpiece is mounted; and
an inertia calculating means for calculating a load inertia based on the torque or electric current command, outputted to the feed shaft motor drive means from the speed control means, and the acceleration of the feed shaft to output the load inertia to the speed control means and the acceleration feed forward control means, the speed control means outputting a desired torque or electric current command based on the load inertia, calculated by the inertia calculating means, to the feed shaft motor drive means.
Further, according to the present invention, there is provided a feed mechanism for moving a moving body of each feed shaft;
a feed shaft motor for driving the feed mechanism;
a feed shaft motor drive means for driving the feed shaft motor;
a numerically controlling means for executing the numerically controlled program data to drive the feed shaft motor by a moving command distribution controlling unit and a servo control unit and for outputting the result of execution to the feed shaft motor through the feed shaft motor drive means;
a data storage means for storing a time constant of acceleration and deceleration of the feed shaft and allowable temperature data for feed shaft motor;
a temperature calculating means for estimating, through an calculation, the temperature of the feed shaft motor based on the torque or electric current command outputted to the feed shaft motor drive means from the servo motor control means;
an acceleration deceleration time constant calculating means for setting an acceleration deceleration time constant based on a comparison between the allowable temperature data previously stored in the data storage means and the temperature of the feed shaft motor estimated by the temperature calculating means to output the resultant time constant to the movement command distribution controlling unit; and
a calculation controlling means for estimating a desired torque command or an electric current command corresponding to a change in the frictional force of the feed mechanism or the weight of a workpiece obtained based on the torque command or the electric current command and the acceleration of the feed shaft outputted from the servo control unit to the feed shaft motor drive means when the feed shaft motor is driven to output the estimated desired torque or electric current command to the feed motor drive means.
In the numerically controlled machine tool of the present invention, according to the movement command outputted from the movement command distributing control unit, it is possible to conduct the detection of start of movement from stoppage, calculation of acceleration by the second order differentiation, feedforward control of speed, and feedforward control of acceleration. Therefore, before the feed shaft motor is driven, control can be conducted by the calculation controlling means. Accordingly, even if the feed speed is high, machining can be conducted with high accuracy.
According to the present invention, the temperature of the feed shaft motor is estimated by calculation and compared with the predetermined temperature data allowed to the feed shaft motor, and the time constant of acceleration and deceleration of the feed shaft is changed according to the result of comparison. Further, the desired torque command or electric current command corresponding to changes in the frictional force of the feed shaft and the weight of a workpiece is outputted into the feed shaft motor drive means. In the present invention, the above control can be conducted being combined.
As described above, according to the present invention, it is possible to provide a method of controlling a numerically controlled machine tool by which machining can be conducted with high accuracy even when a moving body of the machine tool is moved at high speed, also it is possible to provide a numerically controlled machine tool by which machining can be conducted with high accuracy even when a moving body of the machine tool is moved at high speed. Even if the quadrant of a feed shaft is changed over while profile machining or curved face machining is being conducted by moving a plurality of feed shafts simultaneously, or even if the weight of a workpiece given to the feed shaft is changed, machining accuracy can be kept high.
Even if a change is caused in the dynamic and static frictional force of the feed mechanism at the inversion of movement of the feed shaft and at the start of movement from stoppage, it is possible to conduct machining with high accuracy. When a workpiece mounted on the moving body of the feed shaft is replaced or an attachment used for attaching the workpiece is replaced and also when the weight of a workpiece is reduced with time while it is being machined, a desired torque command or electric command is outputted into the feed shaft motor drive means while it follows a change in inertia caused by the change in the weight. Therefore, the machining accuracy can be kept high. Further, even when the feed shaft motor is continuously operated being frequently accelerated and decelerated, there is no possibility of overheat of the feed shaft motor. Accordingly, machining can be conducted with high accuracy.
The present invention is compared with the aforementioned five prior arts as follows. According to the first prior art, various accelerations caused by lost motions are added to the speed command of the servo control unit, and the feed shaft motor is driven via the speed control unit after that. On the other hand, according to the present invention, the desired torque command or electric current command is estimated by calculation, and the result of estimation is directly outputted into the feed motor shaft drive means. Therefore, the feed shaft motor can be driven without causing any delay. According to the second prior art, there still exists a delay in servo system of the positional feedback controlling means and the speed feedback controlling means. However, according to the present invention, the above delay is not caused. According to the third prior art, acceleration of the feed shaft is controlled so that it can be lowered. On the other hand, according to the present invention, acceleration of the feed shaft is kept at an appropriate predetermined value, and a desired torque command or electric current command is outputted into the feed shaft motor drive means when a value of inertia is changed. Therefore, the machining efficiency is not be deteriorated. According to the fourth prior art, the torque observer detects a change in the load torque estimated by the speed command, and the load inertia is estimated. On the other hand, according to the present invention, load inertia is calculated by using the torque command or electric current command actually outputted into the feed shaft motor drive means. Therefore, more actual load inertia can be found, and an accurate torque command can be outputted into the feed shaft motor drive means. The fifth prior art relates to a technique for preventing the feed shaft motor from overheating. On the other hand, according to the present invention, a desired torque command or electric current command corresponding to changes in the frictional force of the feed mechanism and the weight of a workpiece is outputted into the feed shaft motor drive means. Therefore, machining can be conducted with high accuracy.